Solvent dewaxing process

ABSTRACT

Lubricating oil of low pour test is produced in a solvent dewaxing process wherein wax-bearing oil is first heated to a temperature above the melting point of the wax contained therein, solvent is admixed with the heated oil, the solvent-oil mixture is cooled to a dewaxing temperature and the wax separated by filtration. Wax and dewaxed oils are recovered as products and solvent is recovered for recycle and reuse in the process. Cold solvent is added to the heated wax-bearing oil to rapidly cool the oil-solvent mixture to a temperature below the temperature of the melting point of the wax contained therein and above the temperature at which wax is crystallized from the oil-solvent mixture. The cooled oil-solvent mixture is then chilled at a final chilling rate of 0.3* to 3.0*F. per hour to a filtration temperature above 10* below the pour point of the dewaxed oil product. The filtration rate is continuously determined and the final chilling rate is controlled in response thereto.

United States Patent 1 1 1 3,764,517 Bodemuller, Jr. Oct. 9, 1973SOLVENT DEWAXING PROCESS [57] ABSTRACT lnvemofi Robert Bodemllller, JNedelland, Lubricating oil of low pour test is produced in a solventdewaxing process wherein wax-bearing oil is first [73] Assignee: TexacoInc. New York NY. heated to a temperature above the melting point of thewax contained therein, solvent is admixed with the Filedl 1, 1970 heatedoil, the solvent-oil mixture is cooled to a de- [21] Appli NOJ 100,070waxing temperature and the wax separated by filtration. Wax and dewaxedoils are recovered as products and solvent is recovered for recycle andreuse in the US. Cl. process olvent is added to the heated wax- [51]Int. Cl. (210g 43/08 bearing il to rapidly cool the oil-solvent mixtureto a [58] Field of Search 208/33 temperature below the temperature ofthe melting point of the wax contained therein and above the tem-References Cited perature at which wax is crystallized from the oil-UNITED STATES PATENTS solvent mixture. The cooled oil-solvent mixture isthen 3,549,514 12/1970 Brown et al. 208/33 chilled at a final chillingrate of Per 3,642,609 2/1972 Mayer et a] r 208/33 to a filtrationtemperature above 10 below the pour 2,410,483 11/1946 Dons et a] 208/33p int f th dewaxed i pr The filtration rate is Primary Examinerl-lelenM. S. Sneed Attorney-Thomas l-l. Whaley and Carl G. Reis continuouslydetermined and the final chilling rate is controlled in responsethereto.

7 Claims, 1 Drawing Figure SOLVENT DEWAXING PROCESS BACKGROUND OF THEINVENTION In many dewaxing plants, the filtration step whereinprecipitated wax is separated from the dewaxed oil is the criticaloperational step in the sense that the filtration operation is thelimiting factor with respect to the capacity of the dewaxing plant. Inmany instances, if

the rate of filtration of the precipitated wax from the dewaxed oil isincreased, the plant capacity for the production of dewaxed oil can beproportionately increased.

In the solvent dewaxing of wax-bearing oils, the waxy oil and solventare customarily mixed and the mixture heated to a temperaturesufficien't to effect complete solution of the waxy oil and solvent. Itis known that the dewaxing filtration rate may be substantiallyincreased by heating the mixture of waxy oil and solvent to atemperature of l to 50F. above the minimum temperature of completesolution prior to beginning chilling as is described in Knowles U.S.Pat. No. 2,137,209.

SUMMARY OF THE INVENTION In accordance with the present invention evenhigher filtration rates are achieved and economy in the required heattransfer is effected by separately heating the waxy oil to a temperatureabove the temperature of the melting point of the wax contained thereinprior to combining with the solvent.

The wax melting point will depend upon the particular stock treated andmay vary, for example, from about 100F. for the wax separated from alight paraffinic lubrication stock such as a spindle distillate to about210F. for the wax separated from a deasphalted residual stock such asbright stock.

Solvent is then added in any suitable manner to the preheatedwax-bearing oil. Advantageously, the solvent employed is at a relativelylow temperature within the range of about 60 to 135F. affectingequilibration of the temperature of the oil-solvent mixture to atemperature within the range of about 80 to 150F. The oilsolvent mixtureis then cooled by indirect heat exchange to a temperature of 0 to F.below the pour point of the desired oil product by indirect heatexchange. Further dilution with solvent in the course of chilling mayalso be effected.

Chilling by dilution of the preheated oil charge with cold solvent iseffected substantially instantaneously, i.e., within the period of about5 to seconds required for complete mixing. By this means, shock chillingat an actual rate of about 100 to 1,000F. per minute is readilyobtained. In chilling the oil-solvent mixture by indirect heat exchange,chilling at a rate of 0.3" to F. per minute is typically employed and isreadily obtainable in scraped wall double pipe heat exchangers.Accordingly, it is an object of this invention to provide an improveddewaxing process. Another object of the invention is to provide animproved process for the dewaxing of waxy lubricating oils. Stillanother object of this invention is to provide a method for increasingthe dewaxing capacity of a dewaxing plant such as a plant for thedewaxing of waxy mineral oils or for the solvent fractionalcrystallization or separation of waxes from mineral oils, fatty acids,vegetable oils, animal oils and fish oils.

An advantage of the process of this invention is that dewaxing may beeffected at higher throughputs than heretofore obtainable whilemaintaining high yields of dewaxed oil and low oil content of theseparated wax. It has been found that the use of the method of thisinvention has resulted in increases of 10 to 30 percent in thethroughput capacity of a given dewaxing facility and uniformly highthroughputs are obtained with variation in solvent compositions.

DESCRIPTION OF THE DRAWING The accompanying drawing diagrammicallyillustrates the application of the present invention to the solventdewaxing of lubricating oil and the separation of oil-free wax. Oilcharge, for example, a wax-bearing mineral oil separated by vacuumdistillation of a paraffin base crude oil is introduced as chargethrough line 1 into heater 2. Heater 2 may be a shell and tube type heatexchanger heated with steam or a hot heat transfer fluid passed throughcoil 3 or advantageously may comprise the charge oil storage tankageheated by means of immersed steam coils. The oil charge is heated inheater 2 to a temperature of at least the melting point of the waxcontained in the charge and preferably to a temperature 5 to F. abovethe melting point of the wax contained in the charge oil. The heated oilis then discharged through line 7. In line 7, the preheated waxy oil isinitially diluted with cold solvent from line 9. The temperature of themixture rapidly equilibrates as the oil charge and solvent streams aremixed in line 7. The resulting mixture of solvent and waxy oil is thenpassed to chiller 12 where the mixture is further cooled by indirectheat exchange to the desired dewaxing temperature. Chiller 12 isdesirably a scraped wall double pipe heat exchanger. It is necessary toprovide means to scrape the walls of chiller 12 since the precipitatedwax would otherwise deposit on the cooling surface and reduce theefficiency of the heat exchange. Cooling is effected by heat exchangewith ammonia, evaporating propane, brine or other means of refrigerationwell known in the art.

Filtrate from the repulp filtration from line 13 is introduced assecondary dilution at an intermediate point in chiller 12. The filtratein line 13 is predominantly solvent and is at the low temperature of therepulp filtration. Slurry of wax particles in cold solvent-oil mixtureis discharged from chiller 12 through line 15 to primary filter 16. Inprimary filter l6, wax is separated by filtration from primary filtratecomprising dewaxed oil and solvent. The dewaxed oil and solvent isdischarged through line 17. Filter cake in primary filter 16 is coldwashed with solvent introduced through line 18 and the resulting filtercake is discharged through line 19. The primary filter cake is repulpedby dilution with additional solvent from line 21 and the resultingslurry of wax in solvent is passed to repulp filter 23. In repulp filter23, occluded oil is washed from the wax particles and the resultingfiltrate is discharged through line 13 for recycle back to chiller 12.The separated wax in repulp filter 23 is cold washed with solvent fromline 25 and the washed wax is then passed through line 26 to solventstripper 27. In solvent stripper 27, solvent is distilled from the waxand product wax is discharged through line 28. Recovered solvent isdischarged through line 29 for recycle and reuse in the process.

Primary filtrate is passed to solvent stripper 31 where the solvent isstripped from the dewaxed oil. Dewaxed oil product is discharged throughline 32. Recovered solvent is discharged from solvent stripper 31through line 35 and is reused with solvent in line 29 to provide thedilution and washing solvent streams employed in the process.

The solvent used in the solvent dewaxing process is of a selective typehaving a substantially complete solvent action upon the oil component ofthe waxy oil charge, and substantially no solvent action upon the waxcontained therein at dewaxing temperatures of about 10 to -30F. Such asolvent comprises, for example, a mixture of an aliphatic ketone, suchas acetone, methyl ethyl ketone or methyl isobutyl ketone and anaromatic hydrocarbon such as benzene, tolu ene, or a mixture of benzeneand toluene. It is contemplated, however, that mixtures of otheraliphatic ketones and aromatic hydrocarbons may be employed, or thataromatic hydrocarbons may be employed by themselves. Such solvents aslow boiling petroleum hydrocarbons including naphtha, gasoline, pentane,or mixtures thereof may be used as may certain hydrocarbon derivativessuch as dichloromethane, methylene chloride, chloroform, and ethers.This invention is particularly adapted to the dewaxing of wax-bearingmineral oil derived from paraffin base crude, examples of which includePennsylvania, East Texas, Rhodesia, paraffinic Venezuelan, and so forth.Such crudes contain about 5 to 50 percent of wax by volume of the oil.

The temperature of the solvent in line 9 is controlled to control thetemperature of the oil-solvent mixture passed to chiller 12. Control ofthis mixture temperature while maintaining a constant chiller outlettemperature provides a means of controlling the differential temperatureacross chiller 12 and hence means for controlling the cooling rate. Thefiltration rate is maximized by measuring the rate of flow of thefiltrate in line 17 by rate of flow meter 40. Rate of flow meter 40generates a signal representative of the filtration rate. Thetemperature of the solvent in line 9 is determined by temperature metercontroller 41 which controls coolant in line 42 passed to cooler 43.Temperature meter controller 41 is reset by the signal from rate of flowmeter 40 to optimize the filtration rate. Optimization is effected witha logic circuit providing a directional signal which includesconventional analog-todigital converters, shift registers,digital-to-analog converters and a comparator whose arrangements arestraight forward and the details of which are not necessary for theunderstanding of the inventions by one skilled in the art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In an example of the process ofthis invention, a lubricating oil stock containing wax having a meltingpoint of I52F. was solvent dewaxed in a comparative test in which threeconsecutive tests, A, B, and C were made. In Tests A and C the oil washeated to a temperature above the melting point of the wax contained inthe charge prior to dilution with solvent and chilling. In Test B, thecharge was heated to a temperature above the cloud and pour point of thecharge stock but below the melting point of the wax contained thereinprior to dilution with solvent and chilling. In each case the pro cesssequence shown in the figure described above was used and the charge,dilution and wash solvent were controlled to give a yield of 82.2percent of dewaxed oil having a F. pour and a yield of 17.8 percent of a152F. melting point deoiled wax. The charge stock used in these testswas a refined wax distillate 40, i.e., a vacuum distillate from aparaffin base crude oil which had been solvent refined with furfural andcontacted with clay to produce a stock used in the manufacture of SAEgrade 40 lubricating oils. Tests on the original charge stock aretabulated in Table I.

TABLE I Refined Wax Distillate 40 Gravity,API 29.5 Viscosity, SUS at100F. 602 SUS at 170F. I I7.5 SUS at 210F. 69.5 Viscosity Index 98.8Pour F. I I5 Wax, l 1.6

Unit operating conditions and product tests on the dewaxed oil anddeoiled wax are given in Table II. The solvent in each test comprised 45volume percent toluene and 55 volume percent methyl ethyl ketone.

TABLE II Unit Operating Conditions Test A Test B Test C Oil charge rate,BPH 208 I79 195 Initial dilution, solv/oil 1.75 1.88 1.78 Secondarydilution, solv/oil 0.75 0.67 0.68 Solvent to repulp dilution, BPH 200146 175 Cold wash to primary filters, BPH I98 I97 195 Cold wash torepulp filters, BPH 71 72 Solvent charge temp., F. 85 85 Oil ChargeTemp., "F. I58 I32 155 Primary Filter Feed Temp., F. 6 7 6 Repulp FilterFeed Temp., F. I5 l3 l2 Dewaxed Oil Product Tests Gravity API 27.1 27.2Viscosity SUS at F. 800 806 800 SUS at 170F. 136.5 137.0 136.4 SUS at210F. 75.4 75.8 75.3 Viscosity Index 86.6 87.0 86.5 Pour, F. I0 I0 10Wax, 1.0 1.5 Deoiled Wax Product Tests Gravity, API 35.7 35.8 Oil, 14.811.2 12.6 Melting Point, T. 151.6 152 152 The unit was operated at theconditions necessary to maintain maximum charge oil rate whilemanufacturing the equivalent oils and waxes. The data in Table IIdemonstrate that much higher filtration rates and hence higher chargeoil rates are obtained upon heating the charge stock to a temperatureabove the melting point of the wax contained therein, as shown in TestsA and C as compared with heating the charge oil to a temperature onlyabove the pour point of the oil as shown in Test B. It should be notedthat a temperature above the pour point of the oil is substantiallyabove the temperature of complete miscibility of the oil and solventsince the solvent has a substantial solvent effect upon the waxy oil.

I claim:

1. A process for the separation of wax from a waxbearing oil whichcomprises separately heating the wax-bearing oil to a temperature abovethe melting point of the wax contained therein, shock-chilling theheated oil at a rate between 100F. and 1,000F. per minute to atemperature between 80F. and F. by the addition of solvent thereto,chilling the resulting oil-solvent mixture at a rate between 0.3F. and3.0F. per minute by indirect heat exchange to a temperature between 0F.and 15F. below the pour point desired in the product oil, filtering thechilled mixture in a primary filtration zone to separate wax from aprimary filtrate comprising dewaxed oil and solvent, separating solventfrom said dewaxed oil, generating a signal in response to the rate offlow of said primary filtrate and controlling the temperature of saidsolvent to be used for the shock-chilling of said heated oil in responseto said signal.

2. The process of claim 1 in which the separated wax is repulped withsolvent and subjected to a second filtration, solvent is stripped fromthe filtered wax and recycled to the primary filtration.

3. The process of claim 1 in which the separated wax is repulped withsolvent and subjected to a second filtration, solvent is stripped fromthe filtered wax and recycled to the repulping step.

4. The process of claim 1 in which the separated wax is repulped withsolvent and subjected to a second filtration, solvent is stripped fromthe filtered wax and recycled to the shock-chilling zone.

5. The process of claim 1 in which the temperature of the solvent to-beused for shock chilling is controlled by indirect heat exchange.

6. The process of claim 5 in which the temperature of the medium usedfor indirect heat exchange with the solvent is controlled in response tosaid signal.

7. The process of claim 1 wherein the temperature of the solvent mixedwith said wax-bearing oil is within the range of about 60 to F.effecting equilibration to a temperature within the range of about 80 toF.

2. The process of claim 1 in which the separated wax is repulped withsolvent and subjected to a second filtration, solvent is stripped fromthe filtered wax and recycled to the primary filtration.
 3. The processof claim 1 in which the separated wax is repulped with solvent andsubjected to a second filtration, solvent is stripped from the filteredwax and recycled to the repulping step.
 4. The process of claim 1 inwhich the separated wax is repulped with solvent and subjected to asecond filtration, solvent is stripped from the filtered wax andrecycled to the shock-chilling zone.
 5. The process of claim 1 in whichthe temperature of the solvent to be used for shock chilling iscontrolled by indirect heat exchange.
 6. The process of claim 5 in whichthe temperature of the medium used for indirect heat exchange with thesolvent is controlled in response to said signal.
 7. The process ofclaim 1 wherein the temperature of the solvent mixed with saidwax-bearing oil is within the range of about 60* to 135*F. effectingequilibration to a temperature within the range of about 80* to 150*F.